The etiology of most personality disorders (PDs) is not well understood. The primary aim of the proposed research is to examine genetic and environmental factors associated with individual differences in symptoms of various PDs and associated maladaptive personality traits, which would provide insights into the etiology of PDs. A second aim is to examine genetic and environmental influences on the covariation of PD features and executive cognitive functioning. Problems in executive cognitive functioning can manifest as impulsivity and poor judgment. Similar problems are characteristic of certain PDs, but the relationship between personality pathology and executive cognitive functioning has not previously been examined. This is important because executive cognitive functioning may play a role in the expression of certain PD symptoms or traits (e.g., impulsivity). The proposed study will examine symptoms of 10 DSM-IV PDs and associated personality traits in 60 MZ and 60 DZ twin pairs. PD symptoms will be assessed with a structured clinical interview that will yield symptom counts. Maladaptive personality traits will be assessed with a comprehensive self-report. Executive cognitive functioning will be indexed by scores from two widely used measures: the Wisconsin Card Sorting Test and the Stroop Color-Word Test.Twins will be recruited from the Florida State University campus and the greater Tallahassee area. Intraclass correlations calculated separately for MZ and DZ twins will be examined to assess genetic and environmental influence on PD symptom counts and self-reported traits and executive cognitive functioning measures. Interclass correlations will quantify the covariation between variables. The genetic contribution to that covariation between PD features and executive cognitive functioning will be assessed through examination of cross twin cross-trait correlations (PD trait of one twin correlated with executive cognitive functioning variable from the co-twin). Structural equation models will be fit to the twin data to provide an estimate of the magnitude of genetic and environmental influences on PD symptoms and associated traits and to the covariation between PD features and executive cognitive functioning. This study will provide insights into the etiology of symptoms and traits associated with various PDs and provide pilot data for larger applications aimed at examining factors that may be involved in the etiology and expression of PDs.